Magnetic device and magnetic random access memory

ABSTRACT

A spin-orbit-torque (SOT) magnetic device includes a bottom metal layer, a first magnetic layer disposed over the bottom metal layer, a spacer layer disposed over the first magnetic layer, and a second magnetic layer disposed over the spacer layer. A diffusion barrier layer for suppressing metal elements of the first magnetic layer from diffusing into the bottom metal layer is disposed between the bottom metal layer and the first magnetic layer.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/135,805 filed Dec. 28, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/427,308 filed May 30, 2019, now U.S. Pat. No.10,879,307, which claims priority to U.S. Provisional Patent ApplicationNo. 62/734,484 filed Sep. 21, 2018, the entire contents of each of whichare incorporated herein by reference.

BACKGROUND

An MRAM offers comparable performance to volatile static random accessmemory (SRAM) and comparable density with lower power consumption tovolatile dynamic random access memory (DRAM). Compared to non-volatilememory (NVM) flash memory, an MRAM offers much faster access times andsuffers minimal degradation over time, whereas a flash memory can onlybe rewritten a limited number of times. One type of an MRAM is a spintransfer torque random access memory (STT-RAM). An STT-RAM utilizes amagnetic tunneling junction (MTJ) written at least in part by a currentdriven through the MTJ. Another type of an MRAM is a spin orbit torqueRAM (SOT-RAM).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a SOT MRAM cell according to anembodiment of the present disclosure.

FIG. 1B is a schematic view of a SOT MRAM cell according to anembodiment of the present disclosure.

FIGS. 2A, 2B, 2C and 2D show schematic cross sectional views ofmanufacturing operations of a SOT MRAM cell according to embodiments ofthe present disclosure.

FIGS. 3A, 3B, 3C and 3D show experimental results of perpendicularmagnetic anisotropy of SOT magnetic devices with and without a diffusionbarrier layer.

FIGS. 4A and 4B show experimental results of secondary ion massspectroscopy.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanying drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of” Further, inthe following fabrication process, there may be one or more additionaloperations in/between the described operations, and the order ofoperations may be changed. In the present disclosure, a phrase “one ofA, B and C” means “A, B and/or C” (A, B, C, A and B, A and C, B and C,or A, B and C), and does not mean one element from A, one element from Band one element from C, unless otherwise described.

In a spin orbit torque type magnetic device, thermal stability ofperpendicular magnetic anisotropy (PMA) is one of the criticalperformance metrics. The perpendicular magnetic anisotropy is affectedby an interface between a spin orbit active layer (e.g., a heavy metallayer) and a free magnetic layer (e.g., a data storage layer). Inparticular, interfacial diffusion may degrade the perpendicular magneticanisotropy performance. Defects and non-ideal structure of the interfacemay result in perpendicular magnetic anisotropy instability and athicker magnetic dead layer (MDL), at which ferromagnetic order is lost.The present disclosure is directed to a novel interface between the spinorbit active layer and the free magnetic layer to solve theaforementioned problems in the SOT magnetic device.

FIG. 1A is a schematic view of a SOT MRAM cell (SOT magnetic device)that utilizes spin-orbit interaction in switching according to anembodiment of the present disclosure.

The SOT magnetic device includes a bottom metal layer 10, as aspin-orbit interaction active layer, formed over a support layer 5.Further, the SOT magnetic device includes a first magnetic layer 20,which is a free magnetic layer or a data storage layer, disposed overthe bottom metal layer 10, a nonmagnetic spacer layer 30 disposed overthe first magnetic layer, and a second magnetic layer 40, as a referencelayer, disposed over the nonmagnetic spacer layer 30. In someembodiments, a top conductive layer 50, as an electrode, is disposedover the second magnetic layer 40. Further, in embodiments of thepresent disclosure, a diffusion barrier layer 100 is disposed betweenthe bottom metal layer 10 and the first magnetic layer 20, as shown inFIG. 1A.

The magnetic moment of the free layer 20 (first magnetic layer) isswitched using the spin-orbit interaction effect. In some embodiments,the magnetic moment of the first magnetic layer 20 is switched usingonly the spin-orbit interaction effect. In other embodiments, themagnetic moment of the first magnetic layer 20 is switched using acombination of effects. For example, the magnetic moment of the firstmagnetic layer 20 is switched using spin transfer torque as a primaryeffect that may be assisted by torque induced by the spin-orbitinteraction. In other embodiments, the primary switching mechanism istorque induced by the spin-orbit interaction. In such embodiments,another effect including, but not limited to, spin transfer torque, mayassist in switching.

The bottom metal layer 10 is a spin orbit active layer that has a strongspin-orbit interaction and that can be used in switching the magneticmoment of the first magnetic layer 20. The bottom metal layer 10 is usedin generating a spin-orbit magnetic field H. More specifically, acurrent driven in a plane through the bottom metal layer 10 and theattendant spin-orbit interaction may result in the spin-orbit magneticfield H. This spin orbit magnetic field H is equivalent to thespin-orbit torque Ton magnetization, where T=−γ[M×H] in the firstmagnetic layer 20. The torque and magnetic field are thusinterchangeably referred to as spin-orbit field and spin-orbit torque.This reflects the fact that the spin-orbit interaction is the origin ofthe spin-orbit torque and spin-orbit field. Spin-orbit torque occurs fora current driven in a plane in the bottom metal layer 10 and aspin-orbit interaction. In contrast, spin transfer torque is due to aperpendicular-to-plane current flowing through the first magnetic layer20, the nonmagnetic spacer layer 30 and the second magnetic layer 40(reference layer), that injects spin polarized charge carriers into thefirst magnetic layer 20. The spin-orbit torque T may rapidly deflect themagnetic moment of the first magnetic layer 20 from its equilibriumstate parallel to the easy axis. The spin-orbit torque T may tilt themagnetization of the first magnetic layer 20 considerably faster thanconventional STT torque of a similar maximum amplitude. In someembodiments, switching can be completed using spin-orbit torque. Inother embodiments, another mechanism such as spin transfer may be usedto complete switching. The spin-orbit field/spin-orbit torque generatedmay thus be used in switching the magnetic moment of the first magneticlayer 20.

In some embodiments, the interaction of the bottom metal layer includesthe spin Hall effect. For the spin Hall effect, a current Je is drivenin the plane of the bottom metal layer 10 (i.e., current-in-plane,substantially in the x-y plane in FIG. 1A). In other words, the currentJe is driven perpendicular to the stacked direction of the filmsincluding the bottom metal layer 10 and the first magnetic layer 20(i.e., perpendicular to the normal to the surface, the z-direction inFIG. 1A). Charge carriers having spins of a particular orientationperpendicular to the direction of current and to the normal to thesurface (z-direction) accumulate at the surfaces of the bottom metallayer 10. A majority of these spin-polarized carriers diffuse into thefirst magnetic layer 20 (free layer). This diffusion results in thetorque Ton the magnetization of the first magnetic layer 20. Sincetorque on the magnetization is equivalent to the effective magneticfield on the magnetization, as set forth above, the spin accumulationequivalently results in the field H on the first magnetic layer 20. Thespin-orbit field for the spin-Hall effect is the cross product of thespin-orbit polarization and the magnetic moment of the first magneticlayer 20. As such, the magnitude of the torque is proportional to in theplane current density Je and spin polarization of the carriers. Thespin-Hall effect may be used in switching the magnetic stacked layershown in FIG. 1A when the polarization induced by the spin-Hall effectis parallel to the easy axis of the first magnetic layer 20. To obtainthe spin-orbit torque T, the current pulse is driven in plane throughthe bottom metal layer 10. The resulting spin-orbit torque T counteractsdamping torque, which results in the switching of the magnetization ofthe first magnetic layer 20 in an analogous manner to conventional STTswitching.

As set forth above, the bottom metal layer 10 is a spin orbit activelayer that causes a strong spin orbit interaction with the firstmagnetic layer 20 (free layer). In some embodiments, the bottom metallayer 10 includes one or more heavy metals or materials doped by heavymetals. In certain embodiments, α-W, β-W and/or β-Ta is used as thebottom metal layer 10. A thickness of the bottom metal layer 10 is in arange from about 2 nm to 20 nm in some embodiments and is in a rangefrom about 5 nm to 15 nm in other embodiments.

The first magnetic layer 20 as a data storage layer is a free layerhaving a magnetic moment that is switchable. The first magnetic layer 20includes a cobalt iron boron (CoFeB) layer, a cobalt/palladium (CoPd)layer and/or a cobalt iron (CoFe) layer having a thickness in a rangefrom about 0.6 nm to about 1.2 nm in some embodiments. In otherembodiments, the first magnetic layer 20 includes multiple layers ofmagnetic materials. In certain embodiments, the first magnetic layer isFe_(x)Co_(y)B_(1-x-y), where 0.50≤x≤0.70 and 0.10≤y≤0.30. In otherembodiments, 0.55≤x≤0.65 and 0.15≤y≤0.25.

The nonmagnetic spacer layer 30 is made of a dielectric material, andfunctions as a tunneling barrier. In some embodiments, the nonmagneticspacer layer 30 includes a crystalline or an amorphous magnesium oxide(Mg0) layer. In other embodiments, the nonmagnetic spacer layer 30 ismade of aluminum oxide or a conductive material, such as Cu. In someembodiments, the nonmagnetic spacer layer 30 has a thickness in a rangefrom about 0.3 nm to about 1.2 nm, and in other embodiments, thethickness of the nonmagnetic layer 30 is in a range from about 0.5 nm toabout 1.0 nm. In this disclosure, an “element layer” or a “compoundlayer” generally means that the content of the element or compound ismore than 99%.

The second magnetic layer 40 is a reference layer of which magneticmoment does not change. In some embodiments, the second magnetic layer40 is made of the same material as the first magnetic layer 20 as setforth above. In some embodiments, the second magnetic layer 40 includesmultiple layers of magnetic materials. In some embodiments, the secondmagnetic layer 40 includes a multilayer structure of cobalt (Co) andplatinum (Pt). In some embodiments, a thickness of the second magneticlayer 40 is in a range from about 0.2 nm to about 1.0 nm and is in arange from about 0.3 nm to about 0.5 nm in other embodiments.

In some embodiments, the second magnetic layer 40 is a multilayerincluding a synthetic antiferromagnetic layer having ferromagneticlayers separated by nonmagnetic layer, such as Ru. In some embodiments,a pinning layer, such as an antiferromagnetic layer that fixes themagnetic moment of the second magnetic layer 40 in place is disposedover the second magnetic layer 40 with a Ru layer interposedtherebetween. The first and second magnetic layers are crystalline insome embodiments.

The top conductive layer 50 as an electrode includes one or more layersof Ta, Ru, Au, Cr and Pt.

The support layer 5 is made of a dielectric material, such as siliconoxide, silicon oxynitride, silicon nitride, aluminum oxide, magnesiumoxide or any other suitable material. In some embodiments, the supportlayer 5 is a shallow trench isolation layer, an interlayer dielectric(ILD) layer or an inter-metal dielectric (IMD) layer in a semiconductordevice.

In the present disclosure, a diffusion barrier layer 100 is disposedbetween the bottom metal layer 10 and the first magnetic layer 20 toimprove an interface property between them. In some embodiments, thediffusion barrier layer 100 can suppress metallic elements in the firstmagnetic layer 20 from diffusing into the bottom metal layer 10. Whenthe first magnetic layer 20 is in direct contact with the bottom metallayer 10, a relatively thick magnetic dead layer is formed and metallicelements, such as Fe and Co, in the first magnetic layer 20 diffuse intothe bottom metal layer by a subsequent thermal process at about 300° C.to about 450° C.

In the present disclosure, as shown in FIG. 1A, a diffusion barrierlayer 100 that suppresses metallic elements in the first magnetic layer20 from diffusing into the bottom metal layer 10 is disposed between thefirst magnetic layer 20 and the bottom metal layer 10. A thickness ofthe diffusion barrier layer is in a range from about 0.1 nm to about 0.6nm in some embodiments, and is in a range from about 0.2 nm to about 0.5nm in other embodiments.

In some embodiments, the first magnetic layer 20 includes iron andcobalt, and thus the diffusion barrier layer 100 suppresses diffusion ofiron and/or cobalt from the first magnetic layer 20 to the bottom metallayer 10. In some embodiments, the diffusion barrier layer 100 is aniron rich layer including iron, and an atomic percentage of iron in thediffusion barrier layer 100 is higher than an atomic percentage of ironin the first magnetic layer 20. In some embodiments, the atomicpercentage of iron in the diffusion barrier layer 100 is higher at thefirst magnetic layer side than at the bottom metal layer side. Incertain embodiments, the amount of iron gradually decreases from thefirst magnetic layer side to the bottom metal layer side.

In some embodiments, the first magnetic layer 20 further includes boron,and the diffusion barrier layer 100 also further includes boron. Anatomic percentage of the boron in the first magnetic layer 20 is thesame as or different from an atomic percentage of the boron in thediffusion barrier layer 100. In certain embodiments, the atomicpercentage of the boron in the diffusion barrier layer 100 is higherthan the atomic percentage of the boron in the first magnetic layer 20.

In some embodiments, the first magnetic layer 20 isFe_(x)Co_(y)B_(1-x-y), as set forth above, and the diffusion barrierlayer 100 is Fe_(z)B_(1-z), where z>x. In some embodiments, 0.50≤x≤0.70,0.10≤y≤0.30 and 0.65≤z≤0.90. In other embodiments, 0.55≤x≤0.65,0.15≤y≤0.25 and 0.65≤z≤0.75.

In some embodiments, the diffusion barrier layer 100 is a cobalt richlayer, and an atomic percentage of cobalt is higher than an atomicpercentage of cobalt in the first magnetic layer 20. In someembodiments, the atomic percentage of cobalt in the diffusion barrierlayer 100 is higher at the first magnetic layer side than at the bottommetal layer side. In certain embodiments, the amount of cobalt graduallydecreases from the first magnetic layer side to the bottom metal layerside.

The diffusion barrier layer 100 may be made of other materials. In someembodiments, the diffusion barrier layer 100 is made of a nonmagneticmetal material, such as magnesium. In other embodiments, the diffusionbarrier layer 100 is made of a dielectric material, such as a metaloxide. In some embodiments, the metal oxide is an oxide of the metalcontained in the bottom metal layer. In certain embodiments, the metaloxide is one of tungsten oxide and tantalum oxide.

FIG. 1B is a schematic view of a SOT MRAM cell according to anotherembodiment of the present disclosure. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described in FIG. 1A may be employed in the followingembodiments, and detailed explanation thereof may be omitted.

Similar to FIG. 1A, a bottom metal layer 10 is formed over a supportlayer 5. In some embodiments, the bottom metal layer 10 is a β-W layer.A first magnetic layer 20, as a free or reference layer, is formed overthe bottom metal layer 10. In some embodiments, the first magnetic layer20 includes iron and cobalt. In certain embodiments, the first magneticlayer 20 further includes boron. A nonmagnetic spacer layer 30 made of,for example, magnesium oxide, is formed over the first magnetic layer20, and a second magnetic layer 40 is formed over the nonmagnetic spacerlayer 30.

In some embodiments, an intermediate metal layer 60 is disposed betweenthe nonmagnetic spacer layer 30 and the second magnetic layer 40. Insome embodiments, the intermediate metal layer 60 is made of anonmagnetic material. In certain embodiments, the intermediate metallayer 60 is made of Mg. A thickness of the intermediate metal layer 60is in a range from about 0.1 nm to about 0.6 nm in some embodiments andis in a range from about 0.2 nm to about 0.5 nm in other embodiments. Inother embodiments, no intermediate metal layer is used.

In some embodiments, an antiferromagnetic layer 70 is formed over thesecond magnetic layer, and a third magnetic layer 80 is formed over theantiferromagnetic layer 70, as shown in FIG. 1B. The anti-ferromagneticlayer 70 helps to fix the magnetic moment of the second magnetic layer40. In some embodiments, the antiferromagnetic layer 70 includesruthenium (Ru) or any other suitable antiferromagnetic material. In someembodiments, the thickness of the antiferromagnetic layer 70 is in arange from about 0.2 nm to about 0.8 nm.

The third magnetic layer 80 includes one or more layers of magneticmaterials. In some embodiments, the third magnetic layer 80 includes oneor more of cobalt, iron, nickel and platinum. In some embodiments, thematerial of the third magnetic layer 80 is the same as or different fromthe material of the second magnetic layer 40. In certain embodiments,the third magnetic layer 80 is a CoPt layer. A thickness of the thirdmagnetic layer is in a range from about 0.5 nm to about 1.5 nm in someembodiments and is in a range from about 0.7 nm to about 1.2 nm in otherembodiments.

Further, as shown in FIG. 1B, a diffusion barrier layer 100 is disposedbetween the bottom metal layer 10 and the first magnetic layer 20, toprevent the metal elements of the first magnetic layer 20 from diffusinginto the bottom metal layer 10. The diffusion barrier layer 100 is oneof an iron rich layer having a higher iron atomic percentage than thefirst magnetic layer, a cobalt rich layer having a higher cobalt atomicpercentage than the first magnetic layer, a magnesium layer, a tungstenoxide layer and a tantalum oxide layer.

In some embodiments, iridium is included in any of the diffusion barrierlayer 100 and the intermediate metal layer. In some embodiments, aniridium containing layer is inserted between any two adjacent layers asshown in FIG. 1B. The iridium containing layer can be one selected fromthe group consisting of an iridium layer, an iridium oxide layer, abilayer structure of an iridium layer and an iridium oxide layer, aniridium-titanium nitride layer, a bilayer structure of an iridium layerand a tantalum layer, and a binary alloy layer of iridium and tantalum.

Each of the layers shown in FIG. 1A and FIG. 1B can be formed bysuitable film formation methods, which include physical vapor deposition(PVD) including sputtering; molecular beam epitaxy (MBE); pulsed laserdeposition (PLD); atomic layer deposition (ALD); electron beam (e-beam)epitaxy; chemical vapor deposition (CVD); or derivative CVD processesfurther comprising low pressure CVD (LPCVD), ultrahigh vacuum CVD(UHVCVD), reduced pressure CVD (RPCVD); electro plating, or anycombinations thereof.

In some embodiments, a film stack is formed by the aforementioned filmformation operations, and after the film stacks are formed, a patterningoperation including one or more lithography and etching operations isperformed on the film stack to form a SOT cell as shown in FIG. 1A.

FIGS. 2A-2C shows a sequential manufacturing operation for forming thediffusion barrier layer 100 according to an embodiment of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after the processes shown by FIGS. 2A-2C, and someof the operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable.

As shown in FIG. 2A, a bottom metal layer 10 is formed over a supportlayer 5. The bottom metal layer 10 can be formed by PVD, CVD, ALD or anyother suitable film formation methods. Then, as shown in FIG. 2B, afirst magnetic layer 20 is formed by using PVD, CVD, ALD or any othersuitable film formation methods. After the first magnetic layer 20 isformed, as shown in FIG. 2B, a magnetic dead layer 22 is formed betweenthe first magnetic layer 20 and the bottom metal layer 10. The magneticdead layer 22 adversely affects the performance of the SOT magneticdevice. The thickness of the magnetic dead layer 22 is in a range fromabout 0.2 nm to about 0.8 nm.

Then, as shown in FIG. 2C, a process to make an iron rich diffusionbarrier layer 100 is performed. In some embodiments, the process is athermal annealing process. A process temperature of the thermalannealing process is in a range from about 350° C. to about 450° C., andis in a range from about 375° C. to 425° C. in other embodiments. Aprocess time of the thermal annealing is in a range from about 30 min toabout 240 min in some embodiments, and is in a range from about 90 minto about 180 min in other embodiments. By the thermal annealing process,an iron rich layer, as the diffusion barrier layer 100, is formed asshown in FIG. 2C. In some embodiments, the thickness of the magneticdead layer 22 decreases. In certain embodiments, after the thermalannealing process, the thickness of the magnetic dead layer 22 is fromabout 0.1 nm to about 0.3 nm. In a specific embodiment, the magneticdead layer 22 disappears.

In other embodiments, a plasma treatment process to make an iron/cobaltrich diffusion barrier layer 100 is performed. After the first magneticlayer 20 is formed as shown in FIG. 2B, the first magnetic layer 20 issubjected to plasma. The plasma is at least one plasma of argon,nitrogen and hydrogen in some embodiments. RF plasma, inductivelycoupled plasma (ICP) or electron-cyclotron resonance (ECR) plasma or anyother plasma can be utilized. In some embodiments, a process time of theplasma treatment is in a range from 1 min to 60 min and is in a rangefrom about 10 min to about 30 min in other embodiments. During theplasma treatment, the stacked structure is heated at a temperature in arange from about 250° C. to about 450° C., in some embodiments. By theplasma treatment, an iron rich layer, as the diffusion barrier layer100, is formed as shown in FIG. 2C. In some embodiments, the thicknessof the magnetic dead layer 22 decreases. In certain embodiments, afterthe plasma treatment, the thickness of the magnetic dead layer 22 isfrom about 0.1 nm to about 0.3 nm. In a specific embodiment, themagnetic dead layer 22 disappears.

Further, when the diffusion barrier layer 100 is an oxide of tungsten ortantalum, the diffusion barrier layer 100 can be formed by directlyoxidizing the surface of the bottom metal layer 10 made or tungsten ortantalum, as shown in FIG. 2D. The oxidation process includes a thermaloxidation process, a plasma oxidation process or a wet chemicaloxidation process. After the oxide of tungsten or tantalum is formed asthe diffusion barrier layer 100, the first magnetic layer 20 is formed.

In other embodiments, the diffusion barrier layer 100 is formed bydeposition methods, such as PVD, CVD, MBE, ALD, electro plating or anyother suitable methods.

FIGS. 3A, 3B, 3C and 3D show experimental results of perpendicularmagnetic anisotropy (perpendicular magnetic anisotropy) of SOT magneticdevices exhibiting effects of the diffusion barrier layer 100 accordingto the present disclosure. In FIGS. 3A-3D, the horizontal direction is amagnetic field (Oe), and the vertical axis is the magneto-optic Kerreffect (MOKE). FIGS. 3A and 3C show perpendicular magnetic anisotropyfor a SOT magnetic cell without a diffusion barrier layer, and FIGS. 3Band 3D show perpendicular magnetic anisotropy for a SOT magnetic cellwith a diffusion barrier layer 100. FIGS. 3A and 3B show theperpendicular magnetic anisotropy as initially formed and FIGS. 3C and3D show the perpendicular magnetic anisotropy after the SOT magneticcell is subjected to a thermal process at 400° C. for 50 min. As shownin FIGS. 3A and 3B, both the SOT magnetic cell without a diffusionbarrier layer and the SOT magnetic cell with a diffusion barrier layershow good perpendicular magnetic anisotropy results having a clearhysteresis. However, after the SOT magnetic cell without a diffusionbarrier layer is heated at 400° C., the perpendicular magneticanisotropy result shows no hysteresis. In contrast, even after the SOTmagnetic cell with a diffusion barrier layer is heated at 400 ° C., agood hysteresis was observed in the perpendicular magnetic anisotropyresult. These results show that the diffusion barrier layer 100according to the present disclosure can improve thermal stability of theSOT magnetic cell.

FIGS. 4A and 4B show experimental results exhibiting effects of thediffusion barrier layer 100 according to the present disclosure. FIGS.4A and 4B are the results by energy dispersive X-ray spectrometry (EDX).Samples used in the EDX analysis include, from the bottom, a siliconoxide support layer, a tungsten layer as a bottom metal layer, a cobaltiron boron layer as a first magnetic layer, a magnesium oxide layer as anonmagnetic spacer layer, a Mg layer as an intermediate metal layer, acobalt iron boron layer as a second magnetic layer, and a Ru layer. Thesample for FIG. 4A further includes an iron boron layer as a diffusionbarrier layer, and the sample for FIG. 4B is the same as for FIG. 4Aexcept it does not include a diffusion barrier layer. The samples aresubjected to a heat treatment at 400° C. for 50 min.

In this experiment, the first and second magnetic layers areFe_(0.6)Co_(0.2)B_(0.2) and the diffusion barrier layer isFe_(0.7)B_(0.3). The thickness of the tungsten layer is about 10 nm, thethickness of the first magnetic layer is about 0.8 nm, the thickness ofthe magnesium oxide layer is about 1.0 nm, the thickness of the Mg layeris about 0.3 nm, the thickness of second magnetic layer is about 0.4 nmand the thickness of the Ru layer is about 3 nm.

As shown in FIG. 4B, significant amounts of iron (Fe) and cobalt (Co)diffuse into the tungsten layer, while as shown in FIG. 4A, diffusion ofiron and cobalt into the tungsten layer is effectively suppressed. Inview of FIGS. 3A-3D and 4A and 4B, by using the diffusion barrier layer100, diffusion of iron and cobalt from the first conductive layer intothe tungsten layer (bottom metal layer) can be effectively suppressed,thereby improving the thermal stability of the SOT magnetic device.

When thermal stability of an SOT magnetic cell is high, it is easier tointegrate the SOT magnetic cell as an MRAM into a semiconductor device.In some embodiments, an MRAM device is formed at a back-end-of-line(BEOL) of the entire semiconductor manufacturing operation. In the BEOL,the structures formed over a semiconductor substrate are subjected toone or more thermal operations from about 400° C. to about 450° C.Accordingly, the SOT magnetic cell of the present disclosure iscompatible with the BEOL process of a semiconductor manufacturingprocess.

In some embodiments, an MRAM cell includes the SOT magnetic device shownin FIG. 1A and a current source 110 and a switching element 120, such asa transistor.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

For example, in the present disclosure, a diffusion barrier layer isinterposed between a bottom metal layer (a spin orbit active layer) anda first magnetic layer (a free magnetic layer). The diffusion barrierlayer suppresses diffusion of a metallic element, such as iron andcobalt, included in the first magnetic layer into the bottom metallayer. Thus, the interface property can be improved. For example, athickness of a magnetic dead layer can be reduced. Further, thediffusion barrier layer specifically suppresses diffusion of themetallic element at a subsequent heating process. Accordingly, the spinorbit torque (SOT) magnetic device of the present disclosure exhibitsimproved perpendicular magnetic anisotropy (PMA), and is compatible witha semiconductor device fabrication process.

In accordance with an aspect of the present disclosure, aspin-orbit-torque (SOT) magnetic device includes a bottom metal layer, afirst magnetic layer disposed over the bottom metal layer, a spacerlayer disposed over the first magnetic layer, and a second magneticlayer disposed over the spacer layer. A diffusion barrier layer forsuppressing metal elements of the first magnetic layer from diffusinginto the bottom metal layer is disposed between the bottom metal layerand the first magnetic layer. In one or more of the foregoing andfollowing embodiments, the first magnetic layer includes iron andcobalt. In one or more of the foregoing and following embodiments, thediffusion barrier layer includes iron, and an atomic percentage of ironin the diffusion barrier layer is higher than an atomic percentage ofiron in the first magnetic layer. In one or more of the foregoing andfollowing embodiments, the first magnetic layer further includes boron,and the diffusion barrier layer further includes boron. In one or moreof the foregoing and following embodiments, an atomic percentage of theboron in the diffusion barrier layer is higher than an atomic percentageof the boron in the first magnetic layer. In one or more of theforegoing and following embodiments, the first magnetic layer isFe_(x)Co_(y)B_(1-x-y), and the diffusion barrier layer is Fe_(z)B_(1-z),where z>x. In one or more of the foregoing and following embodiments,0.50≤x≤0.70 and 0.65≤z≤0.90. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer includes cobalt, andan atomic percentage of cobalt in the diffusion barrier layer is higherthan an atomic percentage of cobalt in the first magnetic layer. In oneor more of the foregoing and following embodiments, the diffusionbarrier layer is made of magnesium. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer is made of an oxideof tungsten or tantalum. In one or more of the foregoing and followingembodiments, the bottom metal layer is made of tungsten or tantalum. Inone or more of the foregoing and following embodiments, a thickness ofthe diffusion barrier layer is in a range from 0.1 nm to 0.6 nm. In oneor more of the foregoing and following embodiments, the SOT magneticdevice further includes an intermediate metal layer disposed between thespacer layer and the second magnetic layer. In one or more of theforegoing and following embodiments, the intermediate metal layer ismade of magnesium and the spacer layer is made of magnesium oxide. Inone or more of the foregoing and following embodiments, the SOT magneticdevice further includes a top metal layer disposed over the secondmagnetic layer. In one or more of the foregoing and followingembodiments, the top metal layer is made of ruthenium. In one or more ofthe foregoing and following embodiments, the second magnetic layerincludes iron, cobalt and boron.

In accordance with another aspect of the present disclosure, aspin-orbit-torque (SOT) magnetic device includes a bottom metal layer, afirst magnetic layer disposed over the bottom metal layer, a spacerlayer disposed over the first magnetic layer, and a second magneticlayer disposed over the spacer layer. A magnetic dead layer is disposedbetween the bottom metal layer and the first magnetic layer, and adiffusion barrier layer for suppressing metal elements of the firstmagnetic layer from diffusing into the bottom metal layer is disposedbetween the magnetic dead layer and the first magnetic layer. In one ormore of the foregoing and following embodiments, the first magneticlayer includes iron and cobalt. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer includes iron, and anatomic percentage of iron in the diffusion barrier layer is higher thanan atomic percentage of iron in the first magnetic layer. In one or moreof the foregoing and following embodiments, the first magnetic layer andthe diffusion barrier layer further include boron. In one or more of theforegoing and following embodiments, an atomic percentage of the boronin the diffusion barrier layer is higher than an atomic percentage ofthe boron in the first magnetic layer. In one or more of the foregoingand following embodiments, the first magnetic layer isFe_(x)Co_(y)B_(1-x-y), and the diffusion barrier layer is Fe_(z)B_(1-z),where z>x. In one or more of the foregoing and following embodiments,0.50≤x≤0.70 and 0.65≤z≤0.90. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer includes cobalt, andan atomic percentage of cobalt in the diffusion barrier layer is higherthan an atomic percentage of cobalt in the first magnetic layer. In oneor more of the foregoing and following embodiments, the diffusionbarrier layer is made of magnesium. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer is made of an oxideof tungsten or tantalum. In one or more of the foregoing and followingembodiments, the bottom metal layer is made of tungsten or tantalum. Inone or more of the foregoing and following embodiments, a thickness ofthe diffusion barrier layer is in a range from 0.1 nm to 0.6 nm. In oneor more of the foregoing and following embodiments, the SOT magneticdevice further includes an intermediate metal layer disposed between thespacer layer and the second magnetic layer. In one or more of theforegoing and following embodiments, the intermediate metal layer ismade of magnesium and the spacer layer is made of magnesium oxide. Inone or more of the foregoing and following embodiments, the SOT magneticdevice further includes a top metal layer disposed over the secondmagnetic layer. In one or more of the foregoing and followingembodiments, the top metal layer is made of ruthenium. In one or more ofthe foregoing and following embodiments, the second magnetic layerincludes iron, cobalt and boron.

In accordance with another aspect of the present disclosure, a magneticmemory includes a SOT magnetic device and a switching element. The SOTmagnetic device includes a bottom metal layer, a first magnetic layerdisposed over the bottom metal layer; a spacer layer disposed over thefirst magnetic layer, and a second magnetic layer disposed over thespacer layer. The switching device is coupled to the bottom metal layeror the second magnetic layer. A diffusion barrier layer for suppressingmetal elements of the first magnetic layer from diffusing into thebottom metal layer is disposed between the bottom metal layer and thefirst magnetic layer. In one or more of the foregoing and followingembodiments, the first magnetic layer includes iron and cobalt. In oneor more of the foregoing and following embodiments, the diffusionbarrier layer includes iron, and an atomic percentage of iron in thediffusion barrier layer is higher than an atomic percentage of iron inthe first magnetic layer. In one or more of the foregoing and followingembodiments, the first magnetic layer and the diffusion barrier layerfurther include boron. In one or more of the foregoing and followingembodiments, an atomic percentage of the boron in the diffusion barrierlayer is higher than an atomic percentage of the boron in the firstmagnetic layer. In one or more of the foregoing and followingembodiments, the first magnetic layer is Fe_(x)Co_(y)B_(1-x-y) and thediffusion barrier layer is Fe_(z)B_(1-z), where z>x. In one or more ofthe foregoing and following embodiments, 0.50≤x≤0.70 and 0.65≤z≤0.90. Inone or more of the foregoing and following embodiments, the diffusionbarrier layer includes cobalt, and an atomic percentage of cobalt in thediffusion barrier layer is higher than an atomic percentage of cobalt inthe first magnetic layer. In one or more of the foregoing and followingembodiments, the diffusion barrier layer is made of magnesium. In one ormore of the foregoing and following embodiments, the diffusion barrierlayer is made of an oxide of tungsten or tantalum. In one or more of theforegoing and following embodiments, the bottom metal layer is made oftungsten or tantalum. In one or more of the foregoing and followingembodiments, a thickness of the diffusion barrier layer is in a rangefrom 0.1 nm to 0.6 nm. In one or more of the foregoing and followingembodiments, the SOT magnetic device further includes an intermediatemetal layer disposed between the spacer layer and the second magneticlayer. In one or more of the foregoing and following embodiments, theintermediate metal layer is made of magnesium and the spacer layer ismade of magnesium oxide. In one or more of the foregoing and followingembodiments, the SOT magnetic device further includes a top metal layerdisposed over the second magnetic layer. In one or more of the foregoingand following embodiments, the top metal layer is made of ruthenium. Inone or more of the foregoing and following embodiments, the secondmagnetic layer includes iron, cobalt and boron.

In accordance with one aspect of the present disclosure, in a method ofmanufacturing a spin-orbit-torque (SOT) magnetic device, a firstmagnetic layer is formed over a bottom metal layer. A spacer layer isformed over the first magnetic layer. A second magnetic layer is formedover the spacer layer. Further, a diffusion barrier layer is formedbetween the first magnetic layer and the bottom metal layer. In one ormore of the foregoing and following embodiments, the diffusion barrierlayer is formed by a thermal annealing performed after the firstmagnetic layer is formed. In one or more of the foregoing and followingembodiments, a process temperature of the thermal annealing is in arange from 350° C. to 450° C. In one or more of the foregoing andfollowing embodiments, a process time of the thermal annealing is in arange from 30 min to 240 min. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer is formed by a plasmatreatment on the first magnetic layer performed after the first magneticlayer is formed. In one or more of the foregoing and followingembodiments, at least one plasma of argon, nitrogen and hydrogen is usedin the plasma treatment. In one or more of the foregoing and followingembodiments, a process time of the plasma treatment is in a range from 1min to 60 min. In one or more of the foregoing and followingembodiments, the first magnetic layer includes iron and cobalt, thediffusion barrier layer includes iron, and an atomic percentage of ironin the diffusion barrier layer is higher than an atomic percentage ofiron in the first magnetic layer. In one or more of the foregoing andfollowing embodiments, the first magnetic layer and the diffusionbarrier layer further include boron. In one or more of the foregoing andfollowing embodiments, an atomic percentage of the boron in thediffusion barrier layer is higher than an atomic percentage of the boronin the first magnetic layer. In one or more of the foregoing andfollowing embodiments, the first magnetic layer is Fe_(x)Co_(y)B_(1-x-y)and the diffusion barrier layer is Fe_(z)B_(1-z), where z>x. In one ormore of the foregoing and following embodiments, 0.50≤x≤0.70 and0.65≤z≤0.90. In one or more of the foregoing and following embodiments,the first magnetic layer includes iron and cobalt, the diffusion barrierlayer includes cobalt, and an atomic percentage of cobalt in thediffusion barrier layer is higher than an atomic percentage of cobalt inthe first magnetic layer. In one or more of the foregoing and followingembodiments, the diffusion barrier layer is formed by a depositionprocess. In one or more of the foregoing and following embodiments, thediffusion barrier layer is made of magnesium. In one or more of theforegoing and following embodiments, the diffusion barrier layer is madeof an oxide of tungsten or tantalum. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer is made by oxidationof the bottom metal layer. In one or more of the foregoing and followingembodiments, the bottom metal layer is made of tungsten or tantalum andthe diffusion barrier layer is made of an oxide of tungsten or tantalum.In one or more of the foregoing and following embodiments, a thicknessof the diffusion barrier layer is in a range from 0.1 nm to 0.6 nm.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a SOT magnetic device, a diffusion barrier layer isformed over a bottom metal layer. A first magnetic layer is formed overthe diffusion barrier layer. A spacer layer is formed over the firstmagnetic layer. An intermediate metal layer is formed over the spacerlayer. A second magnetic layer is formed over the intermediate metallayer. The diffusion barrier layer suppresses metal elements of thefirst magnetic layer from diffusing into the bottom metal layer in asubsequent thermal process exceeding 450° C. In one or more of theforegoing and following embodiments, the diffusion barrier layer isformed by a thermal annealing performed after the first magnetic layeris formed. In one or more of the foregoing and following embodiments, aprocess temperature of the thermal annealing is in a range from 350° C.to 450° C. In one or more of the foregoing and following embodiments, aprocess time of the thermal annealing is in a range from 30 min to 240min. In one or more of the foregoing and following embodiments, thediffusion barrier layer is formed by a plasma treatment on the firstmagnetic layer performed after the first magnetic layer is formed. Inone or more of the foregoing and following embodiments, at least oneplasma of argon, nitrogen and hydrogen is used in the plasma treatment.In one or more of the foregoing and following embodiments, a processtime of the plasma treatment is in a range from 1 min to 60 min. In oneor more of the foregoing and following embodiments, the first magneticlayer includes iron and cobalt, the diffusion barrier layer includesiron, and an atomic percentage of iron in the diffusion barrier layer ishigher than an atomic percentage of iron in the first magnetic layer. Inone or more of the foregoing and following embodiments, the firstmagnetic layer and the diffusion barrier layer further include boron. Inone or more of the foregoing and following embodiments, an atomicpercentage of the boron in the diffusion barrier layer is higher than anatomic percentage of the boron in the first magnetic layer. In one ormore of the foregoing and following embodiments, the first magneticlayer is Fe_(x)Co_(y)B_(1-x-y) and the diffusion barrier layer isFe_(z)B_(1-z), where z>x. In one or more of the foregoing and followingembodiments, 0.50≤x≤0.70 and 0.65≤z≤0.90. In one or more of theforegoing and following embodiments, the first magnetic layer includesiron and cobalt, the diffusion barrier layer includes cobalt, and anatomic percentage of cobalt in the diffusion barrier layer is higherthan an atomic percentage of cobalt in the first magnetic layer. In oneor more of the foregoing and following embodiments, the diffusionbarrier layer is formed by a deposition process. In one or more of theforegoing and following embodiments, the diffusion barrier layer is madeof magnesium. In one or more of the foregoing and following embodiments,the diffusion barrier layer is made of an oxide of tungsten or tantalum.In one or more of the foregoing and following embodiments, the diffusionbarrier layer is made by oxidation of the bottom metal layer. In one ormore of the foregoing and following embodiments, the bottom metal layeris made of tungsten or tantalum, and the diffusion barrier layer is madeof an oxide of tungsten or tantalum. In one or more of the foregoing andfollowing embodiments, a thickness of the diffusion barrier layer is ina range from 0.1 nm to 0.6 nm.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a SOT magnetic device, a first magnetic layer is formedover a bottom metal layer. The first magnetic layer is treated so that adiffusion barrier layer is formed between the bottom metal layer and thefirst magnetic layer. A spacer layer is formed over the first magneticlayer. An intermediate metal layer is formed over the spacer layer. Asecond magnetic layer is formed over the intermediate metal layer. Thediffusion barrier layer suppresses metal elements of the first magneticlayer from diffusing into the bottom metal layer in a subsequent thermalprocess exceeding 450° C. In one or more of the foregoing and followingembodiments, the diffusion barrier layer is formed by a thermalannealing performed after the first magnetic layer is formed. In one ormore of the foregoing and following embodiments, a process temperatureof the thermal annealing is in a range from 350° C. to 450° C. In one ormore of the foregoing and following embodiments, a process time of thethermal annealing is in a range from 30 min to 240 min. In one or moreof the foregoing and following embodiments, the diffusion barrier layeris formed by a plasma treatment on the first magnetic layer performedafter the first magnetic layer is formed. In one or more of theforegoing and following embodiments, at least one plasma of argon,nitrogen and hydrogen is used in the plasma treatment. In one or more ofthe foregoing and following embodiments, a process time of the plasmatreatment is in a range from 1 min to 60 min. In one or more of theforegoing and following embodiments, the first magnetic layer includesiron and cobalt, the diffusion barrier layer includes iron, and anatomic percentage of iron in the diffusion barrier layer is higher thanan atomic percentage of iron in the first magnetic layer. In one or moreof the foregoing and following embodiments, the first magnetic layer andthe diffusion barrier layer further include boron. In one or more of theforegoing and following embodiments, an atomic percentage of the boronin the diffusion barrier layer is higher than an atomic percentage ofthe boron in the first magnetic layer. In one or more of the foregoingand following embodiments, the first magnetic layer isFe_(x)Co_(y)B_(1-x-y) and the diffusion barrier layer is Fe_(z)B_(1-z)where z>x. In one or more of the foregoing and following embodiments,0.50≤x≤0.70 and 0.65≤z≤0.90. In one or more of the foregoing andfollowing embodiments, the first magnetic layer includes iron andcobalt, the diffusion barrier layer includes cobalt, and an atomicpercentage of cobalt in the diffusion barrier layer is higher than anatomic percentage of cobalt in the first magnetic layer. In one or moreof the foregoing and following embodiments, the diffusion barrier layeris formed by a deposition process. In one or more of the foregoing andfollowing embodiments, the diffusion barrier layer is made of magnesium.In one or more of the foregoing and following embodiments, the diffusionbarrier layer is made of an oxide of tungsten or tantalum. In one ormore of the foregoing and following embodiments, the diffusion barrierlayer is made by oxidation of the bottom metal layer. In one or more ofthe foregoing and following embodiments, the bottom metal layer is madeof tungsten or tantalum and the diffusion barrier layer is made of anoxide of tungsten or tantalum. In one or more of the foregoing andfollowing embodiments, a thickness of the diffusion barrier layer is ina range from 0.1 nm to 0.6 nm.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A magnetic random access memory (MRAM), comprising: a bottom metal layer; a first magnetic layer disposed over the bottom metal layer; a spacer layer disposed over the first magnetic layer; a second magnetic layer disposed over the spacer layer; a diffusion barrier layer disposed between the bottom metal layer and the first magnetic layer; and a magnetic dead layer disposed between the diffusion barrier layer and the bottom metal layer.
 2. The MRAM of claim 1, wherein the diffusion barrier layer and the first magnetic layer includes a same element, and an atomic percentage of the same element in the diffusion barrier layer is higher than an atomic percentage of the same element in the first magnetic layer.
 3. The MRAM of claim 2, wherein the same element is at least one of iron, cobalt or boron.
 4. The MRAM of claim 2, wherein the same element is iron and boron.
 5. The MRAM of claim 1, wherein: the first magnetic layer is Fe_(x)Co_(y)B_(1-x-y), and the diffusion barrier layer is Fe_(z)B_(1-z), where z>x.
 6. The MRAM of claim 5, wherein 0.50≤x≤0.70 and 0.65≤z≤0.90.
 7. The MRAM of claim 1, wherein a thickness of the diffusion barrier layer is in a range from 0.1 nm to 0.6 nm.
 8. The MRAM of claim 1, further comprising a top metal layer made of Ru and disposed over the second magnetic layer.
 9. A magnetic random access memory (MRAM), comprising: a support layer; a bottom metal layer disposed over the support layer; a first magnetic layer disposed over the bottom metal layer; a spacer layer disposed over the first magnetic layer; a second magnetic layer disposed over the spacer layer; a layer made of one of magnesium, tungsten oxide, tantalum or tantalum oxide disposed between the bottom metal layer and the first magnetic layer.
 10. The MRAM of claim 9, wherein the layer includes an oxide of tungsten or tantalum.
 11. The MRAM of claim 9, wherein a thickness of the layer is in a range from 0.1 nm to 0.6 nm.
 12. The MRAM of claim 9, wherein the bottom metal layer is made of one of α-W, β-W or β-Ta.
 13. The MRAM of claim 9, wherein a thickness of the bottom metal layer is in a range from 2 nm to 20 nm.
 14. The MRAM of claim 9, wherein the first magnetic layer is Fe_(x)Co_(y)B_(1-x-y), where 0.50≤x≤0.70 and 0.6≤z≤0.90.
 15. The MRAM of claim 9, wherein the support layer includes silicon oxide.
 16. A method of manufacturing a spin-orbit-torque (SOT) magnetic device, the method comprising: forming a diffusion barrier layer over a bottom metal layer; forming a first magnetic layer over the diffusion barrier layer; forming a spacer layer over the first magnetic layer; and forming a second magnetic layer over the spacer layer, wherein the method further comprising between the first magnetic layer and the bottom metal layer, wherein the diffusion barrier layer includes an oxide.
 17. The method of claim 16, wherein the diffusion barrier layer is formed by directly oxidizing the bottom metal layer.
 18. The method of claim 16, wherein the diffusion barrier layer is formed by thermal oxidation, plasma oxidation or chemical oxidation.
 19. The method of claim 16, wherein the diffusion barrier layer is formed by a deposition method.
 20. The method of claim 16, wherein the diffusion barrier layer includes an oxide of tungsten or tantalum. 